There are seven known cancer viruses, two of which (Kaposi's sarcoma herpesvirus, KSHV/HHV8, and Merkel cell polyomavirus, MCV) were discovered by my laboratory. This R35 application will consolidate currently funded research in my laboratory and provide resources to complete currently unfunded research. It focuses on three main areas: 1) Merkel cell polyomavirus-related cancer and oncogenesis: MCV is the first polyomavirus known to cause human cancer. We are investigating the basic mechanisms used by this virus to regulate cap-dependent translation, to modulate cellular signaling pathways and to dysregulate the cell cycle. Our findings have direct relevance to Merkel cell carcinoma (MCC) but also apply to other noninfectious cancers as well. Ongoing NCI funding on this topic will be incorporated into the R35 award. 2) The role of oncoprotein translation variability in KSHV oncogenesis: We find that LANA1 undergoes a unique form of previously undescribed repeat +1 frameshifting at internal repeat sequences. This reveals that the major oncogene for KSHV expresses previously unknown proteins that could contribute to cell proliferation. Understanding the molecular mechanism for this frameshifting may have relevance to neurodegenerative diseases caused by cellular gene frameshift recoding through a similar mechanism. 3) New ways to find new human cancer viruses: We developed digital transcriptomic subtraction to discover MCV in MCC. Combining transcriptome information with proteomic analyses is a promising approach to discovering additional new agents. This may be particularly important for persistent viral infections in which viral proteins have reduced turnover to prevent host immune recognition. Under these circumstances, viral RNA levels can be miniscule - limiting the ability to detect the agent - while highly stable viral proteins may be abundant. This proposal supports both basic and translational research on new ways that viruses can induce human cancers. I anticipate that it will lay a basis for new insights into methods to reliably determine the role of viruses in human cancers and to uncover novel common cancer pathways that are at work in both infectious and noninfectious tumors.